Most of your assignments will require the image to have PHOTOGRAPHIC INTEGRITY.
This will be our working definition for photographic integrity:The final image appears as it did in the real world.
You can make small changes in contrast, sharpness, saturation. You can remove small imperfections (lint, blemishes, hair, etc).
You can't change the color of things, remove objects, duplicate objects, etc.
The idea is to take great pictures, not make them. Use Photoshop to fine tune, not try to fix a bad image (that never works anyway).